Nullness issue - Spurious(?) 3261 warning with rec module

### Issue description

The following module generates a 3261 warning:
```
module rec M

open System.Collections.Generic

[]
type Hole = Hole of string with
member this.Value =
let (Hole value) = this in value

type Substitution = Dictionary
```

If you change the first line to `module M`, there is no warning.

### Choose one or more from the following categories of impact

- [x] Unexpected nullness warning (false positive in nullness checking, code uses --checknulls and langversion:preview).
- [ ] Missing nullness warning in a case which can produce nulls (false negative, code uses --checknulls and langversion:preview).
- [ ] Breaking change related to older `null` constructs in code not using the checknulls switch.
- [ ] Breaking change related to generic code and explicit type constraints (`null`, `not null`).
- [ ] Type inference issue (i.e. code worked without type annotations before, and applying the --checknulls enforces type annotations).
- [ ] C#/F# interop issue related to nullness metadata.
- [ ] Other (none of the categories above apply).

### Operating System

Windows (Default)

### What .NET runtime/SDK kind are you seeing the issue on

.NET SDK (.NET Core, .NET 5+)

### .NET Runtime/SDK version

.NET 10

### Reproducible code snippet and actual behavior

_No response_

### Possible workarounds

_No response_